I used to live in Studio City, CA back in the 90's.
I knew a guy who made it big in the cigar industry, which was booming back then. When he made his first $1M, he bought one of these new. I think that they were like $100K back then.

take a look at the rennlist classifieds. lots of the "for sale" ads have typical phrases of what work has been done on the car, what the car needs, and typical problems. i was taking a look a while back and it looked to me that owning a 964 is expensive to do right, and big money when they leak.

The air-cooled Porsches are all going up in value as well, I was just looking at prices on 964's I can't believe how much they have gone up in the last few years. I have tried to buy cars (my toys) that hold their value. The 850 is a great car and I'd love to have one, and if I had the money I might look at one but my 993 IMHO is a real keeper for me and I wouldn't give it up for the 850 as nice as it is.

im not sure how much value E31 will hold over the years.. 964 will go higher every year more likely.. if this is not the case, they re a bit different cars.. if you bored, but cant afford 964 at the same time go ahead life is short.. but just a small perspective change for you maybe, you might consider 993 as well instead of 964..

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"Race car driving is like sex. All guys think they're good at it." Jay Leno

There are about 18 964's I am attaching one of the cheaper ones with similar milage and it seems to be in similar condition. The Porsche seems to be holding it's value better but there are so many factors to consider. I'm not disparaging either car or their values BTW.

If you looking for raw classic experience the 964 for sure, the 8 series is to modern and complex, on the cost elements currently the expectations are that they subject to drop in price that is the 964, but not sure this will happen as they being consumed by the like of Singer and others in converting them to earlier 911 looks and all, and it is the 911 model with the shortest life spam before being replaced with 993, so produced in low numbers compare to others.
If you can afford both of them, as in investment I believe the 964 will be worth more purely down to the simplicity and reliability and of course the badge and air cooled old tech no longer around. I keep the 8 series as it is also an appreciating asset providing it is running fine as I believe they tend to demand a lot of work and complexity make them expensive to maintain, all be it probably the same as a Porsche.

Do NOT sell that 8er on a whim. You'll regret it later and might not be able to buy it back. What a gorgeous specimen and if it's your project it has way more sentimental value than dollars can possibly represent.

Different cars. The porsche is a sports car, a car that is driven. It's not a classic. It probably won't rise in value unless you are buying a GT2, GT3 or something more unique. The 850 probably doesn't command high end porsche prices, but it's probably going to rise in value if it's a legitimate CSI. If you treat it nice it'll be a decent investment. If you don't plan on keeping the 850 for the uniqueness and investment aspect, then get rid of it and get something you'll enjoy.

I agree that they are different cars, but the Air-cooled Porsche's continue to go up in value.